1. Field of the Invention
This invention is directed to novel tracers for the determination of flow patterns in subterranean formations.
2. Description of the Prior Art
In recovery of petroleum or minerals from subterranean formations, especially by chemical flooding, one must be knowledgeable about the flow patterns of the formation prior to injection of chemicals. Tracers are used in such reservoir engineering. In the actual recovery process, during chemical injections, it is advantageous to follow the flow of each slug by using a tracer in the slug. Ideally, a tracer should be water soluble and inert to the solids and liquids in the formations. By inert is meant that it does not get absorbed onto the rocks; it does not partition into the oil phase; and it does not interact with the organics and minerals present in the formations. When injected with a chemical, it should also be inert to the chemical it is injected with. A tracer should also be easily and accurately detected by methods which are not interfered by any substance present in the connate fluids.
The tracers now employed are radioactive isotopes and compounds like potassium iodide, ammonium thiocyanate and dichromate. Radioactive isotopes are expensive and require special handling by licensed personnel. Potasium iodide and alike are detected by wet analyses and, therefore, bear the limitations of such analyses.